This invention relates to a control device for a fuel injection system and more particularly to an improved method and apparatus for controlling the fuel injection of an engine at low speeds.
As is well known, low speed running is one of the most difficult conditions to maintain good and stable engine performance and also maintain the low emission of hydrocarbons and other unwanted constituents in the exhaust system. These problems are particularly acute in conjunction with two cycle internal combustion engines because of the fact that the intake charge enters the chamber at the same time that the exhaust charge is being discharged. Under low speed conditions, there is a relatively high residual amount of exhaust gases in the engine and this can adversely affect low speed running. Therefore, it is a common practice with two cycle engines to provide a somewhat wider throttle opening at idle conditions than with four cycle engines.
The aforenoted problems are particularly magnified in conjunction with the use of the engine in a marine propulsion unit such as an outboard motor. Outboard motors frequently are called upon to operate at long periods of time at speeds that are actually less than idle. For example, during trolling it is the normal situation for the engine to operate at a speed even lower than idle speed. The aforenoted problems, as should be readily apparent, become particularly critical at this condition.
When the wider than throttle opening is utilized at idle in a two cycle engine, actual engine speed is controlled by controlling the spark timing rather than the throttle valve condition. However, the amount of fuel injected is controlled not only in response to throttle valve position but also in response to other factors such as engine load. This can give rise to a situation which is known as "hunting" or substantial over or under speed conditions when the load changes as may be understood best by reference to FIG. 1.
FIG. 1 is a graphically view showing engine speed, fuel injection amount, outside load and engine timing when operating at a trolling condition and as the running time progressively continues. As may be seen with a conventional engine, as shown by the broken line curves, when the outside load increase and the throttle position is maintained constant, the engine speed will fall off. However, as the engine speed is decreased than also the amount of fuel injected will be decreased since the engine speed is one of the control parameters. As a result, the decrease in engine speed will be magnified. In a same manner, as the load is decreasing, the engine speed will tend to increase and accordingly the amount of fuel injected will also increase, thus magnifying the over speed condition.
It is, therefore, a principal object to this invention to provide an improved method and apparatus for controlling the fuel injection system of an engine.
It is a still further objection to this invention to provide an improved method and apparatus for controlling the speed of an engine under load speed conditions.
It is a further object to this invention to provide an improved method and apparatus for engine speed control.